Canola oil presently is commercially available which consists of approximately 6 percent saturated fatty acids primarily in the form of stearic acid (C18:0) and palmitic acid (C16:0), approximately 62 percent by weight oleic acid (C18:1) which contains a single double bond per molecule, approximately 22 percent by weight linoleic acid (C18:2) which contains two double bonds per molecule, approximately 10 percent by weight linolenic acid (C18:3) which contains three double bonds per molecule, and less than one percent by weight erucic acid (C22:1) which contains a single double bond per molecule.
Over the years scientists have worked to improve the fatty acid profile for rapeseed oil. Initially the erucic acid (C22:1) composition of rapeseed oil was reduced to produce what is often termed to be "canola" oil. The oxidative stability of the vegetable oil is related to the number of double bonds in its fatty acids. Molecules with several double bonds are recognized to be less stable. Thus, scientists also have worked to reduce the content of linolenic acid (C18:3) in order to improve shelf life and oxidative stability, particularly upon exposure to heat. This has not proved to be possible through the use of naturally occurring germplasm and the reported values for linolenic acid (C18:3) for such germplasm have been greater than 6 percent by weight (e.g., greater than 6 up to approximately 12 percent by weight). As reported by Gerhard Robbelen in Chapter 10 entitled "Changes and Limitations of Breeding for Improved Polyenic Fatty Acids Content in Rapeseed" from "Biotechnology for the Oils and Fats Industry" edited by Colin Ratledge, Peter Dawson, and James Rattray, American Oil Chemists' Society (1984), a mutagenesis experiment was able to achieve lines with less than approximately 3.5 percent by weight of linolenic acid (C18:3) based upon the total fatty acid content. The profiles of these lines indicated that nearly all of the linolenic acid was being directed to linoleic acid (C18:2) and that the levels of oleic acid (C18:1) increased only one or two percent. Nevertheless the oil appeared to offer some advantages over normal canola oil. For instance, the refining process required less hydrogenation than normal canola oil and it exhibited a superior fry life.
Studies have established the value of monounsaturated fatty acids as a dietary constituent. This has led to the popularization of the "Mediterranean Diet," with its emphasis on olive oil, a naturally occurring high source of oleic acid (C18:1). Such a diet is thought to avoid the problem of arteriosclerosis that results from the consumption of saturated fatty acids. However, even in this diet olive oil is thought to be less than ideal, due to its level of saturates. Canola oil is potentially a superior dietary oil, since it contains approximately one-half the saturated fat content of olive oil.
Mutagenesis techniques have been disclosed in the technical literature for increasing the oleic acid (C18:1) content of endogenously formed canola oil over that typically encountered. See in this regard the teachings of U.S. Pat. Nos. 5,625,130 and 5,638,637; European Patent No. 0323753; and International Publication Nos. WO90/10380 and WO92/03919.
Also, approaches involving genetic engineering have been utilized to modify the fatty acid profile of the oil that is endogenously formed in rapeseeds. See, for instance, International Publication No. WO 93/11245, and the Hitz et al. article appearing in the Proceedings of the Ninth International Rapeseed Congress, Cambridge, UK, Vol. 2, Pages 470 to 472 (1995).
Heretofore, it commonly has been observed that when a rape plant is provided that endogenously forms a vegetable oil having an oleic acid content (C18:1) of at least 80 percent by weight that such plant also exhibits less than optimum agronomic performance. Such reduced agronomic performance often is manifest by reduced plant vigor, a later flowering propensity, a lesser number of seed pods per plant, a lesser number of seeds per pod, a lesser overall plant yield, a smaller number of leaves per plant, a lesser total leaf area per plant, a lesser plant height, and a requirement for more time for the plant to reach full maturity. This reduced agronomic performance must be weighed against the improved character of the endogenously formed vegetable oil with respect to oleic acid production that is made possible by such plants.
It is an object of the present invention to provide an improved plant breeding process for forming Brassica napus F.sub.1 hybrid seed having an enhanced commercial value attributable to a combination of (1) the atypical fatty acid profile of the endogenously formed seeds, and (2) the seed yield.
It is an object of the present invention to provide an improved plant breeding process for forming Brassica napus F.sub.1 hybrid seed which exhibits a highly elevated oleic acid (C18:1) content.
It is a further object of the present invention to provide an improved process for forming Brassica napus F.sub.1 hybrid seeds which exhibit a highly elevated oleic acid (C18:1) content and when planted can be grown to form rape plants associated with high oleic acid production which are free from the agronomic shortcomings commonly encountered in the prior art with rape plants that yield such an elevated oleic acid content.
These and other objects and advantages as well as the scope, nature, and utilization of the claimed invention will be apparent to those skilled in the art from the following detailed description and appended claims.